Blower system and method for controlling the same

Abstract

A blower system, including a permanent magnet motor and a wind wheel. The permanent magnet motor includes a stator assembly, a rotor assembly, and a motor controller. The rotor assembly includes a salient pole rotor including a rotor core and magnets embedded in the rotor core. The motor controller includes a microprocessor, a frequency inverter, and a sensor unit. The sensor unit inputs a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor. The microprocessor outputs a signal to control the frequency inverter which is connected to a winding of the stator assembly. The ratio between an air gap of the motor and the thickness of the magnets ranges from 0.03 to 0.065, and the ratio between the length of a pole arc and the length of the magnets ranges from 0.8 to 1.0.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119 and the Paris Convention Treaty, this application claims the benefit of Chinese Patent Application No. 201210179372.6 filed May 31, 2012, the contents of which, including any intervening amendments thereto, are incorporated herein by reference. Inquiries from the public to applicants or assignees concerning this document or the related applications should be directed to: Matthias Scholl P.C., Attn.: Dr. Matthias Scholl Esq., 14781 Memorial Drive, Suite 1319, Houston, Tex. 77079.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a blower system and a method for controlling the same.

2. Description of the Related Art

Variable speed blowers are widely used for heating, ventilation, and air control (HVAC). The impellers of the blower rotate under the drive of a variable speed permanent magnetic motor, and the permanent magnetic motor is driven by an electric control system, that is, a motor controller. As shown in a block diagram of a current variable speed blower system of FIG. 1, the system includes an HVAC product controller, a motor controller, a permanent magnetic motor, and a blower. The HVAC product controller, which is commonly a high level product control panel, outputs an input command to control the operation of the whole product. The input command includes different operation modes of the motor, such as a constant torque mode, a constant rotational speed mode, or a constant air volume mode.

The motor controller includes a microprocessor that is used to receive the input commands and to operate the motor in a torque control mode, or a speed control mode, or in a more advanced mode, for example, air volume control mode. The motor controller further includes a frequency inverter and a sensing circuit. The frequency inverter produces a pulse width modulation (PWM) wave corresponding to different operation modes, and energizes a three-phase winding of a stator. The microprocessor detects operating current and voltage of the motor and receives feedback information through the sensing circuit, and sends out a specific control command to control the operation of the motor.

Conventional variable speed blowers employ a rotor including surface-mounted magnetic tiles. FIG. 2 shows a characteristic curve of the torque-speed of a typical variable speed blower. When the rotational speed of the motor is increased, the torque is required to increase. Thus, when the rotational speed reaches a maximum value, the corresponding torque requires a maximum torque. As shown in FIG. 2, in an operating position W1 with the maximum rotational speed S1, the rotor has the maximum torque T1. For a motor including surface mounted permanent magnets, the operating position W1 is a critical point where the frequency inverter is saturated, because the maximum rotational speed requires the maximum torque, which in turn requires a saturated voltage.

When designing a motor, the required rated torque and the rotational speed are generally considered, as shown in the curve of FIG. 2. However, optimizing the controlling strategies is seldom mentioned to extend the maximum rotational speed and torque of a motor. Furthermore, most of the motors have position sensors, thereby resulting in high material and production costs, and potential circuit failure and system efficiency reduction.

Currently, a typical motor controller employs a sensorless vector control mode, and focuses on the current vector control. However, the patent does not disclose any descriptions about using a control strategy combining the saliency of the salient pole rotor with the high flux density to improve the torque density and lower the production cost; or descriptions about the switch of a torque current control module or a direct stator flux vector control (SFVC) module according to the motor operation to improve the efficiency and lower the production cost.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is one objective of the invention to provide a blower system. In the same rated rotational speed and torque, the blower system can lower the manufacturing cost; optimize the performance, save the energy consumption.

To achieve the above objective, in accordance with one embodiment of the invention, there is provided a blower system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor. The permanent magnet motor comprises a stator assembly comprising a winding, a rotor assembly, and a motor controller. The rotor assembly comprises a salient pole rotor comprising a rotor core and magnets embedded in the rotor core. The motor controller employs a sensorless vector control mode; the motor controller comprises a microprocessor, a frequency inverter, a sensor unit, and other related peripheral circuits. The sensor unit senses a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor. The microprocessor outputs a command signal to control the frequency inverter. The frequency inverter is connected to the windings of the stator assembly. A unique rotor design in structure dimensions is critical to produce the amplitude and shape of motor airgap flux density waveform. Specifically, It is requires that a ratio between an air gap of the motor and a thickness of the magnets ranges from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranges from 0.8 to 1.0.

In a class of this embodiment, the salient pole rotor comprises a rotor core and a permanent magnet, the rotor core comprises an annular ring having a central axial bore and a plurality of magnetic induction blocks protruding outwards from an outer side of the annular ring; between two adjacent magnetic induction blocks is formed a radial recess for receiving the permanent magnets; and a hook block protrudes from the magnetic induction blocks at both sides of an opening of the radial recess.

In a class of this embodiment, the section of an outer side surface of the magnetic induction blocks is a circular-arc line and the outer side surface employs a point with a distance deviating from the center of the central axial bore as a center of circle.

In a class of this embodiment, the number of magnetic poles of the rotor is 8, 10, or 12.

Advantages of the blower system are summarized below:

• • 1) The system employs a structure of salient pole rotor, due to the saliency of the motor, the ratio between the air gap and the thickness of the magnets ranges from 0.03 to 0.065; the saliency L_q/L_d of the salient pole rotor is 1.3-1.7, the length ratio between the pole arc and the magnets is 0.8-1.0. Based on the magnetic flux gathering effect generated by two permanent magnets having the same poles, the surface air gap flux density of the salient pole rotor ranges from 0.6 to 0.8 Tesla. By improving the torque density and improving the flux density through the salient pole structure or by substituting the ferrite magnets with the original Nd—Fe—B magnets, the production costs can be reduced meanwhile the motor performance is remained.
  • 2) The control strategy increases the output torque due to the contribution of the reluctance torque. Under the flux weakening control, the torque is employed to increase the torque and the rotational speed, the operating position of the permanent magnet motor is initiated from W1 to W2. Correspondingly, the output torque T is increased from T1 to T2, and the rotational speed S is increased from S1 to S2. Thus, the motor performance is improved, in other words, the blower system has low production cost and is energy-saving.
  • 3) The invention employs a sensorless vector control mode, thus, the production cost is further decreased.

It is another objective of the invention to provide a method for controlling a blower system. The method can enlarge the torque and the rotational speed, in another word, it can lower the manufacturing cost, optimize the performance, and save the energy consumption.

A first technical scheme of the method for controlling a blower system is summarized herein below:

A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly. A unique rotor design in structural dimensions is critical to produce the sinusoidal waveform of airgap flux density. Specifically, it is requires a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0. An output torque T_torque of the salient pole permanent magnet motor is dependent on a sum of the main field torque K_fI_q and the torque (L_d−L_q)·I_dI_q; and an algorithm control program of the microprocessor takes advantage of contributions of a reluctance torque (L_d−L_q)·I_dI_q to improve the output torque T_torque.

In a class of this embodiment, under a flux weakening control, the microprocessor employs a torque to increase the output torque T_torque, an operating position of the permanent magnet motor is initiated from W1 to W2, correspondingly, the output torque T_torque is increased from T1 to T2, and a rotational speed S is increased from S1 to S2.

A second technical scheme of a method for controlling a blower system is summarized:

A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0. The method comprises: providing the microprocessor with a torque current control module and a direct stator flux vector control (SFVC) module, detecting operating parameters and operating conditions of the motor by the microprocessor, calculating and determining whether the frequency inverter is in a saturated state; controlling the operation of the motor by the torque current control module if the frequency inverter is not saturated; or controlling the operation of the motor by the direct SFVC module if the frequency inverter is saturated.

In a class of this embodiment, the torque current control module works in an operating mode of a maximum torque per ampere (MTPA).

In a class of this embodiment, the direct SFVC module works in an operating mode of a maximum torque per volt (MTPV).

In a class of this embodiment, the microprocessor further comprises a stator flux observer by which a flux, a flux angle, and a load angle are calculated and input into the direct SFVC module.

A third technical scheme of a method for controlling a blower system is summarized:

A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or 12; and the method comprises steps as follows:

• • 1) determining a critical speed S1 at the moment that the frequency inverter is saturated, and inputting the critical speed S1 to the microprocessor;
  • 2) providing the microprocessor with a torque current control module and a direct SFVC module, detecting whether an actual speed S is higher than the critical speed S1 by the microprocessor;
  • 3) controlling the operation of the motor by the torque current control module if the actual speed S is no higher than the critical speed S1; or
  • 4) controlling the operation of the motor by the direct SFVC module if the actual speed S is higher than the critical speed S1.

A fourth technical scheme of a method for controlling a blower system is summarized:

A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or 12; and the method comprising steps as follows:

• • 1) determining a critical torque T1 at the moment that the frequency inverter is saturated, and inputting the critical torque T1 to the microprocessor;
  • 2) providing the microprocessor with a torque current control module and a direct SFVC module, detecting whether an required torque T is larger than the critical torque T1 by the microprocessor;
  • 3) controlling the operation of the motor by the torque current control module if the required torque T is no larger than the critical torque T1; or
  • 4) controlling the operation of the motor by the direct SFVC module if the required torque T is larger than the critical torque T1.

A fifth technical scheme of a method for controlling a blower system is summarized:

A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or 12; the microprocessor comprising a torque current control module, a direct SFVC module, and a stator flux observer; and the method comprising steps as follows:

• • 1) reading a required torque;

  • A torque-rotational speed characteristic curve of an inner permanent magnet motor of a motor system of the invention is shown in FIG. 6. The conventional strategy is that, the motor runs at a base rotational speed S1 at the operating position W1, the frequency inverter is saturated at the base rotational speed S1, thus, it cannot provide with anymore current to produce a larger torque. Compared with the conventional strategy, the example provides an inner permanent magnet motor having a salient pole rotor; the output torque is increased due to the contributions of the reluctance torque. Under a flux weakening control, the microprocessor employs a torque to increase the output torque T_torque, the operating position of the permanent magnet motor is initiated from W1 to W2. Correspondingly, the output torque T_torque is increased from T1 to T2, and the rotational speed S is increased from S1 to S2.

    The blower system employing the salient pole permanent magnet motor, not only improves the torque density, but also decreases the production cost by controlling the saliency of the motor. Furthermore, by the control strategy, the output torque is increased due to the contribution of the reluctance torque. Under the flux weakening control, the lifting torque is employed to increase the torque and the rotational speed, the operating position of the permanent magnet motor is initiated from W1 to W2. Correspondingly, the output torque T is increased from T1 to T2, and the rotational speed S is increased from S1 to S2. Thus, the motor performance is improved, in another word, the blower system has low production cost and is energy-saving.

    EXAMPLE 2

    A method for controlling a blower system is shown in FIGS. 4 and 7. The system comprises a permanent magnet motor and a wind wheel driven by the permanent magnet motor. The permanent magnet motor comprises a stator assembly, a rotor assembly, and a motor controller. The rotor assembly comprises a salient pole rotor comprising a rotor core and magnets embedded in the rotor core. The motor controller employs a sensorless vector control mode and comprises a microprocessor, a frequency inverter, and a sensor unit, of them, the sensor unit inputs a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputs a signal to control the frequency inverter; the frequency inverter is connected to a winding of the stator assembly. A ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0. The number of magnetic poles of the rotor is 8, 10, or 12. The method comprises:

    • • providing the microprocessor with a torque current control module and a direct SFVC module, detecting operating parameters and operating conditions of the motor by the microprocessor, calculating and determining whether the frequency inverter is in a saturated state;
      • controlling the operation of the motor by the torque current control module if the frequency inverter is not saturated; or
      • controlling the operation of the motor by the direct SFVC module if the frequency inverter is saturated.

    The torque current control module works in an operating mode of a maximum torque per ampere MTPA.

    The direct SFVC module works in an operating mode of a maximum torque per volt MTPV.

    The microprocessor further comprises a stator flux observer by which a flux, a flux angle, and a load angle are calculated and input into the direct SFVC module.

    EXAMPLE 3

    A method for controlling a blower system is shown in FIGS. 6 and 7. The system comprises a permanent magnet motor and a wind wheel driven by the permanent magnet motor. The permanent magnet motor comprises a stator assembly, a rotor assembly, and a motor controller. The rotor assembly comprises a salient pole rotor comprising a rotor core and magnets embedded in the rotor core. The motor controller employs a sensorless vector control mode and comprises a microprocessor, a frequency inverter, and a sensor unit, of them, the sensor unit inputs a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputs a signal to control the frequency inverter; the frequency inverter is connected to a winding of the stator assembly. A ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0. The number of magnetic poles of the rotor is 8, 10, or 12. The method comprises:

    • • 1) determining a critical speed S1 at the moment that the frequency inverter is saturated, and inputting the critical speed S1 to the microprocessor;
      • 2) providing the microprocessor with a torque current control module and a direct SFVC module, detecting whether an actual speed S is higher than the critical speed S1 by the microprocessor;
      • 3) controlling the operation of the motor by the torque current control module if the actual speed S is no higher than the critical speed S1; or
      • 4) controlling the operation of the motor by the direct SFVC module if the actual speed S is higher than the critical speed S1.

    EXAMPLE 4

    A method for controlling a blower system is shown in FIGS. 6 and 7. The system comprises a permanent magnet motor and a wind wheel driven by the permanent magnet motor. The permanent magnet motor comprises a stator assembly, a rotor assembly, and a motor controller. The rotor assembly comprises a salient pole rotor comprising a rotor core and magnets embedded in the rotor core. The motor controller employs a sensorless vector control mode and comprises a microprocessor, a frequency inverter, and a sensor unit, of them, the sensor unit inputs a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputs a signal to control the frequency inverter; the frequency inverter is connected to a winding of the stator assembly. A ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0. The number of magnetic poles of the rotor is 8, 10, or 12. The method comprises:

    • • 1) determining a critical torque T1 at the moment that the frequency inverter is saturated, and inputting the critical torque T1 to the microprocessor;
      • 2) providing the microprocessor with a torque current control module and a direct SFVC module, detecting whether an required torque T is larger than the critical torque T1 by the microprocessor;
      • 3) controlling the operation of the motor by the torque current control module if the required torque T is no larger than the critical torque T1; or
      • 4) controlling the operation of the motor by the direct SFVC module if the required torque T is larger than the critical torque T1.

    EXAMPLE 5

    A method for controlling a blower system is shown in FIGS. 8a and 8b. The system comprises a permanent magnet motor and a wind wheel driven by the permanent magnet motor. The permanent magnet motor comprises a stator assembly, a rotor assembly, and a motor controller. The rotor assembly comprises a salient pole rotor comprising a rotor core and magnets embedded in the rotor core. The motor controller employs a sensorless vector control mode and comprises a microprocessor, a frequency inverter, and a sensor unit, of them, the sensor unit inputs a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputs a signal to control the frequency inverter; the frequency inverter is connected to a winding of the stator assembly. A ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0. The number of magnetic poles of the rotor is 8, 10, or 12. The microprocessor comprising a torque current control module, a direct SFVC module, and a stator flux observer. The method comprises:

    • • 1) reading a required torque;

      • V_s,max is dependent on the PWM strategy and the transient DC bus voltage V_dc.

        From the formula (8), it is known that the operation of voltage limitation is to limit the stator flux.

        $\begin{array}{cc}\begin{array}{c}{\lambda }_{\lim }=\frac{\sqrt{V_{\mathrm{smax}}^2-{\left(R_s·i_{\mathrm{sd}}\right)}^2}-R_s·\left|i_{\mathrm{qs}}\right|}{\left|\omega \right|}\\ \cong \frac{V_{s,\max }-R_s·\left|i_{\mathrm{qs}}\right|}{\left|\omega \right|}\end{array}{V}_{s,\max }=V_{\mathrm{dc}}/\sqrt{3}& \left(9\right)\end{array}$

        As shown in FIG. 15, a block diagram for producing a maximum q-axis current, and limitations of the current and the load angle in the MTPV control strategy of the lifting torque is shown. In order to transmit the required torque, the q-axis current is calculated from the torque/current production module in FIG. 10. However, the q-axis current is limited by the maximum current of the frequency inverter. The required current of the q-axis is bidirectionally controlled by the current limiter.

        The q-axis current is limited by the maximum current of the frequency inverter, and the maximum current of the q-axis q_s is defined as:

        $\begin{array}{cc}{i}_{\mathrm{qs},\max }\le \sqrt{I_{s,\max }^2-i_{\mathrm{ds}}^2}& \left(10\right)\end{array}$

        the i_ds is the stator current of the d_s-axis.

        In process of increasing the torque under high speed, the optimal control strategy is to maximize efficiency of the usable phase voltage to achieve a lowest current. In order to realize the strategy, the conditions for motor operation requiring to open or close the maximum load angle are defined as MTPV operation. The maximum load angle is acquired by the analyses of the load angle, which comprises an imitation and an acceleration test. The determination of the maximum load angle improves the stability of the motor, which is like the limitation of the load angle. As shown in FIG. 15, the limitation of the load angle is accomplished by the PI controller, thus the maximum allowable current is lowered.

        As shown in FIG. 16, in a low speed range, the motor controller is in an operating mode of MTPA, a section of the curve is labeled as (0, W1), and the current vector is ISW1. As the speed increases, the frequency inverter becomes saturated, the motor operates in a curve of MTPV operating mode, that is, the section (W1, W2), and the current vector is W2. Thus, the maximum torque and rotational speed is achieved, and the control mode is efficient and energy saving. The current vector IWn is a current transition vector from W1 to W2. As shown in FIG. 16, the section of the curve is very short, which means, the transition part is very efficient, and energy-saving.

        Descriptions of FIGS. 9-16 are specifically summarized in some textbooks, and will not be summarized herein.

        While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

1. A blower system, comprising:

a) a permanent magnet motor, the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; and

b) a wind wheel driven by the permanent magnet motor;

2. The blower system of claim 1, wherein

the rotor core comprises an annular ring comprising a central axial bore, and a plurality of magnetic induction blocks protruding outwards from an outer side of the annular ring;

between two adjacent magnetic induction blocks is formed a radial recess for receiving permanent magnets; and

a hook block protrudes from the magnetic induction blocks at both sides of an opening of the radial recess.

3. The blower system of claim 2, wherein

a section of an outer side surface of the magnetic induction blocks is a circular-arc line; and

the outer side surface employs a point with a distance deviating from the center of the central axial bore as a center of circle.

4. The blower system of claim 3, wherein a number of magnetic poles of the rotor is 8, 10, or 12.

5. A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or 12; and the method comprising:

providing the microprocessor with a torque current control module and a direct stator flux vector control (sfvc) module, detecting operating parameters and operating conditions of the motor by the microprocessor, calculating and determining whether the frequency inverter is in a saturated state; wherein, the direct sfvc module is adapted to adjust a d-axis voltage V_d of the motor in a rotor coordinate according to flux in the stator assembly; and

controlling the operation of the motor by the torque current control module if the frequency inverter is not saturated; or

controlling the operation of the motor by the direct sfvc module if the frequency inverter is saturated.

6. The method of claim 5, wherein the torque current control module works in an operating mode of a maximum torque per ampere (MTPA).

7. The method of claim 5, wherein the direct sfvc module works in an operating mode of a maximum torque per volt (MTPV).

8. The method of claim 5, wherein the microprocessor further comprises a stator flux observer by which a flux, a flux angle, and a load angle are calculated and input into the direct sfvc module.

9. A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or 12; and the method comprising steps as follows:

1) determining a critical speed S1 at the moment the frequency inverter is saturated, and inputting the critical speed S1 to the microprocessor;

2) providing the microprocessor with a torque current control module and a direct sfvc module, detecting whether an actual speed S is higher than the critical speed S1 by the microprocessor; and

3) controlling the operation of the motor by the torque current control module if the actual speed S is no higher than the critical speed S1; or

4) controlling the operation of the motor by the direct sfvc module if the actual speed S is higher than the critical speed S1.

10. A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or 12; and the method comprising steps as follows:

1) determining a critical torque t1 at the moment the frequency inverter is saturated, and inputting the critical torque t1 to the microprocessor;

2) providing the microprocessor with a torque current control module and a direct sfvc module, detecting whether an required torque t is larger than the critical torque t1 by the microprocessor; and

3) controlling the operation of the motor by the torque current control module if the required torque t is no larger than the critical torque t1; or

4) controlling the operation of the motor by the direct sfvc module if the required torque t is larger than the critical torque t1.

11. A method for controlling a blower system, the system comprising a permanent magnet motor and a wind wheel driven by the permanent magnet motor; the permanent magnet motor comprising a stator assembly comprising a winding, a rotor assembly, and a motor controller; the rotor assembly being a salient pole rotor comprising a rotor core and magnets embedded in the rotor core; the motor controller employing a sensorless vector control mode, the motor controller comprising a microprocessor, a frequency inverter, and a sensor unit; the sensor unit inputting a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor, and the microprocessor outputting a signal to control the frequency inverter, the frequency inverter being connected to the winding of the stator assembly; a ratio between an air gap of the motor and a thickness of the magnets ranging from 0.03 to 0.065, and a ratio between a length of a pole arc and a length of the magnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or 12; the microprocessor comprising a torque current control module, a direct sfvc module, and a stator flux observer; and the method comprising steps as follows:

1) reading a required torque;

2) determining ad-axis a d-axis inductance L_d, and a q-axis inductance L_q in the state of magnetic saturation;

3) outputting a stator flux, a flux angle, and a load angle by the stator flux observer;

4) calculating a reference flux based on an operating mode of a maximum torque per ampere (MTPA);

5) calculating a limited flux based on an operating mode of a maximum torque per volt (MTPV);

6) determining whether the limited flux is larger than the reference flux;

7) calculating the voltage V_q according to the requirement of the torque, and calculating the voltage V_d in the operating mode of MTPA if the limited flux is larger than the reference flux and the frequency inverter is not saturated; or

calculating the voltage V_q according to the requirement of the torque, and calculating the voltage V_d in the operating mode of MTPV if the limited flux is no larger than the reference flux; and

8) converting the voltages V_d and V_q into voltages V_α and V_β in a stationary coordinate, converting the voltages V_α and V_β in the stationary coordinate into three-phase voltages V_a, V_b, and V_c, and modulating a PWM using the three-phase voltages V_a, V_b, and V_c.